Aggregation of sand-dune soil by endomycorrhizal fungi

The mycorrhizal fungus Glomus in association with bean hosts (Phaseolus vulgaris L.) was the dominant factor in the aggregation of sand particles in sterilized dune soil artificially inoculated either with Glomus, or with Glomus and a soil extract containing miscellaneous microorganisms. The weight of sand adhered to roots harvested from dried soil was about 3 times greater in mycorrhizal than in nonmycorrhizal roots. The weight of sand aggregates per kilogram dried soil from among roots of senescent beans was 10 g in nonmycorrhizal plants but 54 g in mycorrhizal plants. The fungitoxicant benomyl prevented mycorrhizal development and markedly restricted sand aggregation on and among roots of beans grown in soil inoculated with Glomus. A soil extract enhanced mycorrhizal development, the amount of sand adhered to mycorrhizal roots, and the extent of sand aggregation among mycorrhizal roots. Based on microscopic observations, the major mechanism linking sand grains in aggregates was the binding of sand to extensive Glomus mycelia.